Investigation of Viscosity's Effects on Continuous Casting of Steel Mold Powders Containing B₂O₃, Li₂O, TiO₂, Fe₂O₃, ZnO and Na₂O

Mold powders are mainly formed of such oxides as SiO2, CaO, Al2O3, Na2O along with F and C. One of the main constitutional composes of mold powders is F, which is utilized in chemical composition of mold powders due to its features of controlling viscosity and producing desired lubrication between solidified steel shell and mold. However, the emission of F through such compositions as HF (g) causes health and environmental problems. The purpose of this research is to decrease, and subsequently substitute, F in chemical composition of a lubricating high speed powder, which is used in continuous casting of steel industry. A combination of Fe2O3 and TiO2 compositions to substitute F in chemical composition of a fluorine-free mold powder was used to meet the purposed of this research. In addition, nine powder samples (A-I) with laboratory scale were prepared. In order to evaluate the samples’ viscosity behavior, groove viscometer test and image analysis software was used and to evaluate the crystalline behavior of samples C and G, XRD and SEM analyses were conducted. The results of these analyses demonstrated that the fluorine-free sample, due to its viscosity resemblance in comparison with molten reference powder and through creation of such crystalline phases as Perovskite (CaTiO3) and Fayalite (Fe2SiO4), will result in viscosity control of the mold powder and therefore optimizing continuous casting conditions. Finally, it is possible to derive that this sample may be an appropriate substitution for the reference powder being utilized in steel continuous casting industry.

Improving mold powder through crystallization using calcium fluoride and manganese oxide for continuous casting of steel

Mold powder is generally made of SiO2 and CaO with little amount of calcium fluoride(CaF_(2))and carbon.Basically,F^(-)has a crucial effect on viscosity and crystallization of the powder.However,emission of toxic materials containing F^(-)constituent such as HF and SiF4 leads to serious environmental pollution.Overall,six powder samples were made during this research to study the effects of such compounds as calcium fluoride(CaF_(2))and manganese oxide(MnO)on the crystallization of mold powder and compare with that of the original mold powder.Having considered the chemical compounds of these six samples,two were finally chosen:powder sample A and powder sample E.The former was a simulated sample of the original mold powder using CaF_(2),and the latter was a less-F^(-)sample in which MnO was used as a substitution for F^(-)in the compounds of the mold powder.In other words,the amount of F^(-)was cut in half comparing to that of the original mold powder.The thermal gravimetric analysis(TGA)was performed on the original mold powder,the simulated sample of the original mold powder and the less-F^(-)sample.The results of the TGA demonstrated the reduction of thermal loss in samples A and E comparing to the original mold powder.On the other hand,the results of differential thermal analysis(DTA)of these three samples,i.e.,original mold powder and samples A and E,demonstrated that melting and crystallization temperatures of the original mold powder were similar to those of samples A and E.Therefore,it can be concluded that samples A and E are potential laboratory-scale substitutions for the original mold powder.